I have been running a set in my 4.0 for about 20K miles with no ill effects. I've pulled them twice to check the burn and they look perfect. I'm running a K&N intake but no other mods yet. I recently purchased a URD MAF Calibrator but not installed yet. If you want my honest feeling on the plug...in the V6, if you are replacing OEM copper you will notice a difference. They are cheaper than iridium plugs, lifespan is the unknown for me though; changing plugs on these is not the most fun thing to do.